Silicone compositions are widely used in the construction industry as well as other industrial applications, such as automotive, electronics, aerospace and consumer markets because these materials possess self-bonding adhesion properties to several types of substrates such as glass, metal, ceramics, fabrics, wood, leather, plastics and paper. In addition, superior properties such as low temperature flexibility, high-temperature stability, good electrical insulation and resistance to chemicals and UV resistance are inherent in silicone-based products. Thus, silicone extrusions are widely used in a variety of applications. A disadvantage of cured silicone compositions, however, is that they are considered to be unpaintable. The low surface energy of the silicone prevents latex or oil based paints to wet the surface of the cured silicone. The paint tend to shrink away from the silicone surface leaving a poor surface appearance commonly referred to in the industry as “fish eyes.”
Attempts to improve paintability of silicone compounds have been made by adding inorganic fillers to the uncured silicone. For example, silicone sealants have been formulated with the addition of acicular, i.e. needle-like, calcium carbonate to the polyorganosiloxane. In such sealants, the acicular particles become oriented on the surface of the sealant during curing. The surface of the cured sealant has improved paintability, but the addition of the acicular calcium carbonate results in other problems such as low elasticity. The generally high loading of calcium carbonate necessary to achieve improved paintability deleteriously affects the elasticity of the silicone sealant such that its tensile elongation is lower than desired.
Plasticizer can be added to counter the negative effect of calcium carbonate on the extensibility of the silicone. However, plasticizers detract from the paintability of the silicone sealant.
It is desirable to provide a curable silicone composition that, once cured, is paintable by many types of coatings. It is also desirable to provide silicone extrusions, sealants, adhesives, and caulks that are paintable over an extended period of time and which maintain the excellent elastomeric and other properties inherent in silicone.